This invention relates to pumps and more particularly to pumping systems for gas turbine engines.
Pumping assemblies for gas turbine engines which embody an impeller pump and a vane pump in an integrated design are known in the art. For example, U.S. Pat. No. 3,851,998 shows such a combination pump with a vane pump constituted by a stationary centrally disposed cam and an annular rotor with radially inwardly directed vanes. In the pump of the patent, the vanes fly off the cam surface when a predetermined speed is attained.
A pump, such as shown in the aforementioned patent, presents numerous manufacturing and design problems. In this respect, it will be appreciated that the manufacture of inwardly facing slots in the rotor is more costly than the provision of outwardly facing slots in a standard vane pump rotor. More important, however, is the fact that the vane pump cavity must be evacuated when only the impeller pump is supplying fuel if fuel heating and power consumption are to be minimized. Heating of the engine fuel will, of course, detract from the fuel's ability to perform the assigned cooling functions without exceeding the maximum safe entrance temperature at the fuel nozzles. Also, it may be necessary to provide for withdrawal of the stationary side plates or plate in order to prevent pump damage and/or friction losses.